Armature for small caliber electromagnetic launch projectile

ABSTRACT

The invention concerns an electromagnetically launched projectile having anrmature comprised of refractory metal washers, each of which being coated with a thin film of cathode emitter material. The low work function metal generated by the heat of arcing rises to the armature surface through the capillaries formed between the armature washers. The arc occuring between the rail of the electromagnetic launcher and the armature is lowered due to the formation of a low voltage metallic discharge. The reduced arc drop lowers the erosion rate on the rails which reduces the rail damage resulting in increased firing rate and longer rail life.

GOVERNMENTAL INTEREST

The invention described herein may be made, used, or licensed by or forthe Government for Governmental purposes, without the payment to me ofany royalties thereon.

BACKGROUND AND FIELD OF THE INVENTION

A small caliber electromagnetic launcher typically comprises aprojectile, a rail launcher and a power generating means. Theelectromagnetic launcher might be a linear induction motor, where theprojectile is accelerated along rails by a J×B force, where J is currentdensity and B is magnetic flux density. To generate such a force howeverrequires current to travel on the rails and pass between the railsthrough a conducting portion of the projectile, this conduction portionbeing known as the projectile armature. The greatest limitation toelectromagnetic launchers however is believed found in the capabilitiesof the armature of the projectile and rails. The arc drop (approximately20 volts) occurring between the rail and armature during launch of theprojectile, with the multi-kiloampere rail current, causes excessiveheating and a material erosion.

Clearly therefore any improvements in such mechanisms that would reducethe erosion, in armature and rail, and other advances to the art andscience of rail gun weapons, would be of significant value for use inthe field.

SUMMARY OF THE INVENTION

The invention concerns a small caliber projectile for electromagneticlaunchers, which reduces projectile armature and rail erosion.

A projectile is presented having a nose; a body portion which functionsas an armature when electromagnetically launched (e.g., as a rail gun);a tail end; and a threaded device which secures the body portion andtail to the nose via a threaded hole. The body portion comprises aseries of washers to which a ring of low-work function material isbonded, the thickness of which determines the separation betweenadjacent washers. The material is a thin film of cathode coating. Thebody portion may also comprise a single solid porous refractory elementwith a low-work function material embedded within its pores, or a stackof coated wafers that could include some fraction of copper uncoatedwafers interdispersed. Accordingly, the arc drop occurring at therail-armature interface is reduced by the emission of surface electronsat low temperatures, thus reducing rail and armature erosion.

OBJECTS OF THE INVENTION

Accordingly, it is an object of this invention to provide an improvedrail gun, capable of withstanding rail and armature erosion.

Another object of the invention is to provide an improved armature for asmall caliber electromagnetic launch projectile weapon.

And even another object of this invention is to provide a projectilearrangement for launching by an electromagnetic launching mechanism.

Other objects and attendant advantages of this invention will becomeapparent from a study of the attached specification and a viewing of thedrawings in which:

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates an electromagnetic launch projectile;

FIG. 2 shows a frontal view of a cathode coated washer;

FIG. 3 shows a side, sectional view of the washer in FIG. 2;

FIG. 4 shows an exploded view of a projectile in accordance with thepresent invention;

FIG. 5A shows a first alternate body portion of a projectile; and

FIG. 5B shows a second alternate body portion for a projectile.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a projectile for launching with electromagnetic launchers.The projectile (10) includes an armature (12) consisting ofapproximately 60 copper washers (14). The washers (14) are stackedtogether and held in place between forward and rear phenolics (18, 20).With such a projectile (10), an arc drop during launch occurs, which atthe multi-kiloampere rail current, causes excessive heating and materialerosion to the rail and armature.

An embodiment according to this invention, is illustrated in FIG. 2. Awasher (22) typically comprised of a refractory metal such as tungsten,molybdenum, tantalum or rhenium is shown in frontal view. Accordingly,the thin film ring (26) is comprised of, a barium, strontium carbonatecathode coating mixture, as one example, deposited on the washer (22)surface.

FIG. 3 shows a cross-section of the FIG. 2 device. Here, it is evidentthat the thin film (ring 26) of thickness (28), normal to the surface ofthe washer (22), will determine the separation between any adjacentwashers. This aspect is discussed with respect to FIG. 4.

FIG. 4 depicts a projectile in accordance with the present invention.The projectile (30) includes a series of washers (22) having thin filmring cathodes (26), the series of washers comprising a body portion. Thefront of the projectile (30) is a nose (32) having a threaded hole (34).A tail section (36) has a hole (38) through which a threaded device (40)passes. The threaded device (40) may comprise a screw or bolt whichmates with the threaded hole (34) of the nose (32) such that the bodyportion (in this embodiment the series of washers (22)) and tail (36)are secured to the nose (32).

The washer stack could be replaced with a porous (FIG. 5a) or waferstructure (FIG. 5b) in which low work function material embedded in arefractory metal matrix, comprises the entire body portion. The low workfunction material is drawn to the surface of the rail-armature interfaceby the heat generated by the electric arcing at the rail-armatureinterface. The low work function material reaches the surface of arail-armature interface to reduce arc drop. The washer stack couldinclude one or more copper uncoated washers interdispersed to providethe optimum benefits of thermal conductivity from the copper and theoptimum amount of electron emission from the coated washers.

An armature realized in accordance with FIG. 4 will reduce rail-armaturearcing losses by lowering the work function of the armature surface.When the cathode material activates the low work function metal (cesium,barium, strontium calcium or strontium) is chemically released. Theseparation between the washers provided by the thickness of the coatingalso functions as a capillary drawing the low work function metaltowards the armature surface. There the low work function metal coatsthe bare refractory metal surface lowering the overall armature workfunction. The washer stack with its layers of thermally isolating thinfilm rings (26) separating individual washers also serve to constrainthe heating of the projectile to the armature region.

A plasma, comprised of electrons and ions, forms in the rail-armatureinterstice having a low arc drop characteristic of an alkali metaldischarge. This plasma will appear behind the projectile as well as theinterstice. The plasma should provide an additional force of theself-generated current density of the plasma interacting with thecurrent it carries. The specific design of the armature and the spacingof the rail-armature interstice will determine the proportunatecontributions of the J×B and/or plasma forces acting on the projectile.

A cathode coating may be easily deposited, by a spray gun, evaporationor through impregnation techniques.

Other substitutions and modifications to the invention will becomeapparent to those skilled in the art, which do not depart from the scopeof the invention.

What is claimed is:
 1. A projectile means, for launching via anelectromagnetic launching means, including:a nose end; a body portionhaving a material comprising a means for providing a low-work functionrelative to the electromagnetic launching means; a tail end; and asecuring means for engaging the nose end, and for securing the bodyportion and tail end to the nose end.
 2. A projectile means as in claim1, the body portion having an orifice through which the securing meanspasses.
 3. A projectile means as in claim 2, the material being porous.4. A projectile means as in claim 3, the body portion comprising onesolid porous element.
 5. A projectile means as in claim 4, the nose endhaving a hole with which the securing means mates.
 6. A projectile meansas in claim 5, the securing means comprising a threaded device, and thehole having threads into which the securing means is threaded to matewith the hole.
 7. A projectile means as in claim 3, the body portioncomprising a series of adjacent wafers.
 8. A projectile means as inclaim 7, the nose end having a hole with which the securing means mates.9. A projectile means as in claim 8, the securing means comprising athreaded device, and the hole having threads into which the securingmeans is threaded to mate with the hole.
 10. A projectile means as inclaim 2, the body portion comprising a series of disc-like meansseparated from one another by the means for providing a low workfunction material.
 11. A projectile means as in claim 10, the disc-likemeans comprising a washer.
 12. A projectile means as in claim 11, themeans for providing a low work function material bonded to at least oneside of each washer.
 13. A projectile means as in claim 12, the meansfor providing a low work function material comprising a thin film ringattached to the washer side toward the circumference of the washer. 14.A projectile means as in claim 13, the ring having a thickness normal tothe washer side, which determines the separation between adjacentwashers.
 15. A projectile means as in claim 14, the nose end having ahole with which the securing means mates.
 16. A projectile means as inclaim 15, the securing means comprising a threaded device, and the holehaving threads into which the securing means is threaded to mate withthe hole.
 17. A projectile means as recited in claim 10, wherein eachsaid washer is formed of refractory metal material with an electronemissive coating on the peripheral area thereof to provide spacingbetween the respective washers.
 18. A projectile means as in claim 10,wherein the disc-like means comprises a plurality of interdispersedrefractory coated washers with copper washers.